Zinc absorption, distribution, excretion, and retention by healthy preterminfants

Zinc (Zn) is an essential nutrient for growth, but little is known about Zn absorption, distribution, excretion, and retention in preterm infants. Nin e infants with gestational age 32 +/- 1 wk (mean +/- SE), birth weight 1.44 +/- 0.08 kg, postnatal age 14 +/- 3 d, on Zn intake of 23 +/- 3 mu mol/kg per d via enteral feeding of preterm formula were studied. A stable Zn isot ope (Zn-70) was administered orally or i.v., and plasma, red blood cells, u rine, and feces were sampled for up to 30 d. Samples were analyzed for Zn b y inductively coupled plasma atomic emission spectrometry and for isotope e nrichment by inductively coupled plasma mass spectrometry. Data were analyz ed by compartmental analysis using the Simulation Analysis and Modeling pro gram, and absorption, distribution, excretion, and retention were calculate d. Absorption was 36 +/- 5% or 7 +/- 1 mu mol/kg per d; distribution in pla sma was 15 +/- 1 mu mol Zn/L and in RBC was 41 +/- 4 mu mol Zn/L; excretion in urine was 0.55 +/- 0.03 mu mol Zn/kg per d and in feces was 17 +/- 3 mu mol Zn/kg per d and retention was 5 +/- 1 mu mol/kg per d. Results show th at healthy preterm infants with Zn intake of 23 mu mol/kg per d and expecte d growth rates (>15 g/kg per d) absorb and retain Zn at rates comparable to in utero accretion. The values for absorption, distribution, and excretion by this population of healthy preterm infants provide a normal range for f uture studies, although further studies are required to determine endogenou s excretion rates in healthy preterm infants. We speculate that these value s can be used to determine whether Zn kinetics are abnormal in sick infants or in infants with slow growth.